In a geological repository for radioactive waste, the corrosion of the ferrous materials, radioactive decay of the waste, radiolysis of organic materials and water, and the microbial breakdown of organic materials will produce gas, the most important of which (by volume) is hydrogen. Depending on the repository concept, the production of these gases may span in excess of 100,000 years, following emplacement of the waste. As gas is produced, it will accumulate, moving away from its source through the combined processes of molecular diffusion and bulk advection. Understanding these processes, the long-term fate of the gas and its impact on the surrounding materials is therefore important in the development of a geological disposal facility (GDF) for radioactive waste.
The purpose of Task A in DECOVALEX-2019 is to better understand the processes governing the advective movement of gas in two low permeability materials: (i) one engineered (compacted bentonite) and (ii) one a potential, natural repository host rock (in this case the Callovo Oxfordian Claystone). Special attention is given to the mechanisms controlling factors such as gas entry and flow, as well as pathway stability and sealing, which will impact barrier performance. To underpin this task, new numerical representations for the quantitative prediction of gas fluxes will be developed. These will be tested against a series of controlled laboratory tests, in a staged manner, building in complexity (both in terms of the experimental and modelling approaches). It is anticipated that the development of these models will provide a valuable tool to assess the impact of gas flow on barrier and host materials, providing information which could be used to support future repository design.
In addition, experience gained through this task is of direct relevance to other clay-based engineering issues where advective gas flow is involved, including: shale gas, hydrocarbon migration, carbon capture and storage, gas storage and landfill design.
Data from a series of flow tests performed on initially saturated samples will be made available to project participants. These long-term tests, performed under carefully controlled laboratory conditions, provide detailed datasets with which to examine gas migration behaviour under steady state conditions. As such, a number of test geometries have been used, ranging in complexity from relatively simple 1-dimensional flow tests (performed under constant volume conditions), to triaxial tests performed on natural samples of Callovo-Oxfordian claystone. To gain insights into the advective movement of gas through these materials, laboratory data will be used to guide and benchmark numerical model development in an iterative process, increasing in model complexity from one test stage to the next.
The initial plan of the task includes 4 distinct stages:
For further information, please contact the task leader, Jon Harrington.